The present invention relates to an audio signal processor for performing various acoustic processing for audio signals.
There have been provided audio signal processors capable of performing a plurality of types of arithmetical operations such as filtering, equalizer processing and sound image localization for audio signals. In this regard, filtering and other arithmetical operations each require a relatively large arithmetic circuit including a multiplier and an accumulator. Therefore, if it is attempted to form an audio signal processor capable of performing complicated signal processing composed of a plurality of arithmetical operations, a circuit therefore becomes extremely large. Moreover, the large circuit leads to high power consumption of the audio signal processor due to operation of the circuit. On the other hand, some audio signal processors perform signal processing by receiving audio signals of a plurality of channels in different formats such as, for example, different sampling frequencies. In this type of audio signal processor, signal processing is performed for input digital audio signals using arithmetic circuits prepared for respective channels, the digital audio signals of the respective channels after the signal processing are D/A converted, and then the signals are mixed and output. Since this type of audio equipment has an arithmetic circuit for each channel, it has also a large-sized circuit for signal processing and is high in power consumption. To resolve these drawbacks, there has been provided an audio signal processor for sequentially performing a plurality of types of arithmetical operations such as filtering and equalizer processing with time sharing control by using a common arithmetic circuit. According to this type of audio signal processor, a single arithmetic circuit is used under the time sharing control, and therefore a compact circuitry is achieved. This type of audio signal processor is disclosed in, for example, Patent Document 1, Japanese Laid-Open Patent Publication (Kokai) No. H12(2000)-122650.
The aforementioned conventional audio signal processor sequentially performs predetermined types of arithmetical operations in the fixed order. Therefore, when it is attempted to provide market with audio signal processors different in contents of audio signal processing conforming to various specifications, there is a need for developing and manufacturing audio signal processors for each of the specifications, thereby increasing development and manufacturing costs problematically. As a method of resolving this problem, there is a method of realizing diverse specifications, for example, by preparing a so-called full-featured audio signal processor, which can perform various arithmetical operations such as filtering, equalizer processing and sound image localization, and then omitting filtering for example in some specifications, but not omitting filtering in other specifications or so. For example, in filtering, the omission of the arithmetical operation can be achieved by a method of setting a filter coefficient for a filtering operation at “1” so as to make digital audio signals pass by the arithmetic circuit. Even if being passed by, however, the arithmetic circuit operates at that time and therefore wasteful power is consumed for unnecessary signal processing problematically.
Audio signal processors capable of performing various signal processing for audio data of a plurality of channels are in widespread use. Focusing on a configuration for signal processing, these audio signal processors can be mainly classified into two types. As shown in FIG. 13, a first audio signal processor has a data path for signal processing for each channel and performs the signal processing for audio data of the respective channels in parallel. As shown in FIG. 14, a second audio signal processor has a single data path common to respective channels and sequentially performs signal processing for audio data of the respective channels with time sharing control by using the single data path. As a technical literature disclosing the second audio signal processor, there is, for example, patent document 2, Japanese Laid-Open Patent Publication (Kokai) No. 2000-122680.
According to the aforementioned first audio signal processor, it is possible to reduce power consumption by deactivating data paths of channels not in use. This audio signal processor, however, has a problem that a data path need be provided for each channel, thereby causing a large-sized processor, by which a chip area becomes large when it is formed by an LSI. According to the second audio signal processor, only a single data path need be provided, thereby enabling a small-sized processor device. Therefore, when it is formed by an LSI, the chip area can be reduced. This audio signal processor, however, always performs operations of all channels even if audio data of only a part of channels is input, and therefore it performs essentially unnecessary operations, thereby consuming wasteful power problematically.